The present invention relates generally to a device for attaching terminal straps and terminal poles to the lugs of a plate group, by casting the straps and poles onto the lugs of a completely assembled plate group for a storage battery cell.
Originally, the lugs for all of the negative and all of the positive electrodes of a storage battery cell were individually (or collectively) soldered to the terminal straps (or bars) of the corresponding polarity. However, today, in the interests of economy, the so-called cast-on-strap (COS) process has become generally accepted for this purpose. In this process, both of the terminal bars and the terminal poles (or intercell connectors) are simultaneously attached to a prefabricated plate group, complete with separators, as follows. The assembled plate group is first retained upside down in a retaining cartridge or holder. The lugs which extend from the plate group are then dipped into casting molds (one for each polarity) filled with molten lead, so that the lugs are first melted, and thereafter solidified with the contents of the mold to form the cast-on strap (bar) portions. After solidification the molten lead later becomes the terminal bar and the terminal pole, which are solidly joined to the plate lugs. To this end, the lead is caused to solidify, by gradually dipping the molds into a still or flowing cooling medium.
Because of the spatial separation between the positive and negative lugs of the plate group, the casting molds combine to form a double mold which, in its working position, can be raised and lowered with respect to the plate group. Conversely, the casting molds can remain stationary, while the lugs are dipped into the molten lead by lowering the plate group into the casting molds.
Practical experience with the COS proces has shown that the casting molds, which contain molten metal corresponding not only to the positive or negative terminal straps but also to the positive or negative terminal poles, are in many cases not optimally suited to the heating requirements of the plate lugs. Non-homogeneous heat exchanges between the lead bars and the dipped lugs may, for example, be expected if the size of the bars is identical, but the number of plate lugs to be received by the positive terminal bar is not equal to the number of plate lugs to be received by the negative terminal bar.
It has already been proposed, in German Patent Application No. P 34 34 941.3, to subject the lugs which are placed at a disadvantage in terms of heat exchange with the melt to delayed cooling with respect to the other lugs, so that their deficiency in terms of heat exchange may be compensated by longer residence in the molten lead.
GB-PS No. 872,938 describes a device for casting terminal bars onto the lugs of a completed plate group using the COS principle, wherein the different numbers of lugs for the two plate polarities and their differing demands for lead are taken into account using two mold cavities of different size in a solid mold block. However, differential cooling of the mold cavities is not possible with this device, which excludes the possibility of presolidification of the terminals before the terminal bars solidify.